The use of communication systems having wireless mobile communication units has become widespread. Wireless communication systems that operate within a cell or coverage area provide several important advantages over conventional wired systems. For example, wireless communication users can communicate in locations where wired service is not available or feasible, such as remote or rugged locations. Additionally, wireless communication users within the cell have much more mobility because the units do not have to be connected to a fixed wired network. These and other favorable characteristics make wireless communications ideally suited for personal, business, military, search and rescue, law enforcement, water vehicle, and other field related applications.
In some applications, it is desirable to maintain consistent periodic communication with one or more other communications units. Such consistent communications are useful in situations have a risk of incapacitation of the user, such as battlefield applications, recreational activities in rugged environments, or civilian search and rescue operations. If the periodic communications from the user cease, a search can be carried out at the last reported location. A variation on this theme could include an automated communications unit that periodically broadcasts a signal to other communication units, such that the signal itself can be employed to locate the user.
If an area is equipped with robust communications infrastructures (e.g., cell towers), there are relatively easy ways to establish and maintain such wireless communications to mobile users, by making use of the infrastructure. However, there are some endeavors where it is necessary to provide such a wireless communications capability even while in an area that does not have such a communications infrastructure, and in such cases it is much more difficult to establish and maintain such wireless communications to mobile users.
Even in areas without such a robust wireless communications infrastructure, there are techniques that have been developed to enable the mobile members of a team to establish and maintain digital communications . . . as long as there are cars, trucks, helicopters, or other similar vehicles available for each user, providing the benefit of large antennas and a large power supply. For example, it is presently required that military vehicles possess the capability to send periodic communications to other military units when active. The availability of large antenna masts, and relatively large amounts of electrical power (from the vehicles alternator, etc.) have permitted feasible implementations based on netted line-of-sight radios, and netted line-of-sight radios combined with satellite data terminals designed for on-the-move operations.
Existing communications systems to and from individual users on a battlefield that are not in or near a vehicle (the military terms these “dismounted” soldiers), however, have suffered from severe technical limitations that impede and degrade tactical operations in significant ways. Existing problem areas include battery life, heat dispersion, electromagnetic interference between closely packed radio frequency components, range, safety, weight, complexity of operation, setup and configuration time, and missing functionality. Similar problems plague electronic communications to small mobile teams in other domains, such as search-and-rescue teams, and law enforcement agents in the field. In some real sense, most of these problem areas derive from the issue of battery life; the severe limitations on battery capacity limit the transmit power, which in turn limits communications range. The same sever limitations on battery capacity also limit the transmit duty cycle (e.g., the duration or percentage of time which a transmitter can be on and transmitting), preventing an individual not in a vehicle from communicating continuously without either receiving new batteries or having access to a battery charger for appropriate mission durations. Current implementations are so inefficient that to carry spare batteries for an entire week's worth of mission would be infeasible.
The fundamental problem with current implementations involves limitations in the present art of how electronic communications are implemented for such teams. Weight, size, and battery life are significant design drivers for how a communications device carried by an individual (e.g., in the hand, in a backpack, or attached to the body by some other means, such as slung from the belt) is designed and implemented. This problem is compounded by the fact that the very applications where dismount communications are most useful are those where the weight and size of the communication device are of the most concern. Most current art uses cell phones or single-channel radios with “push-to-talk” channel access for dismounted users. Cell phones clearly will not work in locations where there are no cell towers. Satellite cell phones achieve only very short battery life. Single-channel radios suffice for occasional communications, but cannot maintain the periodic communication required by the applications discussed above at any significant range.